Many systems make use of signal strength to guess at how far away a calibrated (transmit signal level) sender is located. Being able to accurately measure the actual distance between devices would be valuable but, until recently, no practical scheme existed which could perform that function with useful precision in small areas.
RADAR (Radio Detection and Ranging) has been used since World War II to measure distance, counting the time between radio transmission of a pulse and reception of the echo (radio time-of-flight). RADAR uses a high-powered radio signal with enough energy that the signal reflected by a passive metal object at a distance still had enough energy to be received back at the RADAR transceiver. Because of the distances involved, thousands of feet to miles, the precision of the timers used in RADAR didn't have to be very good. The speed of a radio message is about 5.4 microseconds per mile. A RADAR set with a one megahertz counter would count about 5.4 ticks per mile. RADAR only worked in long distances and with very poor precision compared to the size of an indoor stage.
Some modern aircraft tracking systems use a scheme with an active transmitter called a transponder. The transponder notices the RADAR radio signal pulse and immediately transmits a complex radio message containing useful information about the aircraft. This supplemental information could even include the latitude and longitude of the aircraft, measured using global positioning system (GPS) equipment, giving redundant information back to the aircraft tracking network.
The challenge of tracking equipment inside a building isn't solved by RADAR or GPS. RADAR is too high energy and GPS is dependent on radio line-of-site with orbiting satellites. However, the transponder mechanism would be useful, if the time-delay between radio signal pulse and transponder response was knowable, and if the time-of-flight could be measured with much greater precision than 70-year-old RADAR technology.
In the ensuing 70 years, radio devices have become smaller and more sophisticated. We can now purchase integrated circuit (IC) radios which cost as little as $1 and which are far more sensitive than the old equipment, and which deliver digital data and receive signal strength. These radio IC chips have been used by tracking systems to provide location resolution with several meter precision. Time-of-flight measurement was still not practical until very recently.
Accordingly, in light of these difficulties associated with conventional solutions, there exists a need for methods, systems, and computer readable media for time-slotted ultra-wide-band object tracking.